High speed microwave switch utilizing gyromagnetic element



June 25, 1963 J. F. ZALESKI 3,095,547

HIGH SPEED MICROWAVE SWITCH UTILIZING GYROMAGNETIC ELEMENT Filed May 28, 1959 3 Sheets-Sheet 1 INVENTOR. JOHN F. ZALESKI ATTORNEY June 25, 1963 J. F. ZALESK] 3,095,547

HIGH SPEED MICROWAVE SWITCH UTILIZING GYROMAGNETIC ELEMENT Filed May 28, 1959 3 Sheets-Sheet z MICROWAVE 49 SOURCE MICROWAVE LOAD INVENTOR. JOHN F. ZALESKI ATTORNEY June 25, 1963 J. F. ZALESKI 3,095,547

HIGH SPEED MICROWAVE SWITCH UTILIZING GYROMAGNETIC ELEMENT Filed May 28, 1959 3 Sheets-Sheet 3 INVENTOR. JOHN F. ZAhESKl ATTORNEY- United States Patent 3,095,547 HIGH SPEED MICROWAVE SWITCH UTILIZING GYRQMAGNETIC ELEMENT John F. Zaleslri, Pleasantville, N.Y., assigncr to General Precision, Inc., a corporation of Delaware Filed May 28, 1959, Ser. No. 816,417 3 Claims. (Cl. $33-$42) This invention relates to high speed microwave switches which operate by abruptly changing the power-carrying properties of a waveguide.

Microwave switches of this description have been used as duplexers for radar apparatus and similar systems wherein a single antenna is used for both transmission and reception. One such switch is the well known transmit-receive, or TR switch, and another an antitransmitreceive, or ATR switch. The present switch serves the same purposes, as well as other purposes, but operates on entirely different principles.

In the present switch a tube of ferrite material is positioned in the longitudinal axis of a waveguide through which microwave energy is to be passed. One or more magnetic field sources located near the ferrite tube generates a unidirectional magnetic field at the ferrite tube. An electrical conductor is positioned in the bore of the ferrite tube with its two ends brought outside of the waveguide, and a switching current, which may have the form of a current step or of a pulse train, is passed through this electrical conductor. When this is done an electrical load at the output end of the waveguide receives microwave energy of greatly changed magnitude during the step or pulse. 7 I

The ferrite tube may be composed of any selected ferrite material such as, for example, ferramic R 1, made by General Ceramics Corp., Keasbey, N .J This material is composed of iron, manganese and magnesium oxides in the molecular proportions of 22Fe O 8MnO and '70MgO.

The operation of the switch is greatly enhanced by applying a conductive wire helix, a series of metal bands, or a dielectric cylinder to the outside surface of the ferrite tube. The waveguide is preferably hollow, and may be either round or rectangular in form, or may be a continuation of a coaxial line. The ferrite tube is supported in such manner that the supports offer minimum impedance discontinuity to the microwave energy carried by the waveguide. Any discontinuities that are offered by the supports and by the two ends of the ferrite tube may be matched or tuned out by two adjustable susceptances positioned in the waveguide, one in front of the ferrite tube and the other behind it. 7

The present invention is useful as a duplexer and to protect radar receiver semiconductor diodes from burnout by the transmitter pulses. The invention may also be employed in connection with a radar antenna to switch the direction of the radiated microwave beam. In all of these uses the high speed operation of the switch gives it an advantage. This speed of operation is indicated by the small waveform deterioration sutfered by modulating pulses transmitted through the switch, this deterioration being only of the order of 0.005 microsecond.

One purpose of this invention is to provide a high speed microwave switch which has no moving parts.

Another purpose of this invention is to provide a device to open or close a microwave circuit at high speed, analogous to a single-throw switch in a wire circuit.

Another purpose is to provide a microwave device to perform the functions of a radar transmit-receive or antitransmit-receive switch but at greatly increased speeds.

3,095,547 Patented June 25, 1963 Still another purpose is to provide a microwave pulse modulator.

Still another purpose is to provide an electrically-operated attenuator for insertion in a microwave transmission line.

A further understanding of this invention may be secured from the detailed description and associated drawings, in which:

FIGURE 1 depicts one form of the invention in which a ferrite component is axially centered in :a round waveguide, the component being penetrated by an axial wire.

FIGURE 2 depicts one form of ferrite component consisting of a ferrite tube wrapped with a wire helix.

FIGURE 3 depicts another form of ferrite component consisting of a ferrite tube surrounded by a number of close-fitting metal bands.

FIGURE 4 depicts another form of ferrite component consisting of a ferrite tube surrounded by, a dielectric sleeve.

FIGURE 5 depicts another embodiment of the invention utilizing a rectangular waveguide shunt T with the ferrite component and the axial wire in its shunt arm.

FIGURE 6 depicts still another embodiment of the invention utilizing a rectangular waveguide containing the ferrite component and surrounded by a magnetizing coil winding. The fer-rite component is supported by an H-rod structure which also serves as the axial conductor and its terminal leads.

Referring now to FIG. 1, a round hollow waveguide 11 is designed to support X-band microwave transmission, for example, at 8800 me. p.s. This waveguide .11 is connected through broad-face transitions to two rectangular waveguides 12 and 13. These waveguides 12 and 13 are terminated in short-circuited stubs 14 and 16, and employ other .conventional devices as required for matching the transitions so that, when microwave energy in the dominant mode is applied to waveguide 12, it is transformed by the transition to the round waveguide 11, through which it is transmitted in the dominant mode or other suitable mode. The energy is then retransformed to the rectangular waveguide dominant mode and transmitted out waveguide 13 to a microwave load.

Although the waveguide 11 is designated as :a round waveguide section, rectangular waveguide may alternatively be employed.

The round waveguide 11 contains a ferrite component 17 centered axially therein. The ferrite component 17 has an axial hole through which runs an electrical wire conductor 18. This wire, in addition to its electrical functions, may support the ferrite component 17 mechanically. Alternatively, the ferrite component 17 may be supported so as to remain centered in the waveguide by electrical insulators which negligibly distort or impede microwave field energy carried by the waveguide. For example, the ferrite component may be supported by one or more polyfoam cylinders.

The wire 18 is led outside the waveguide system through choke fittings 19 and 21, the metal pipe extensions 22 and 23 of which serve, together, with the coaxial wire 18, to form two pairs of coaxial conductors 24 and 26 forming external terminals for the wire centered in the ferrite component.

The ferrite component 17 consists of a ferrite tube made, for example, of ferramic R-l as more specifically described above, and having a length of one and a half inches, an external diameter of one-quarter inch and a bore diameter of one-eighth inch. Two short permanent magnets in tube form are applied to the two ends of the ferrite tube, with opposed magnetic fields, as depicted by the magnets 27 and 28, FIG. 2. .These magnets are secured by mortising and cementing to the two ends of the ferrite tube 29. The ferrite tube 29 is wrapped with an external helix or bare copper wire 31, closely fitted directly thereto and in mechanical and electrical contact therewith. The end 32 and 33 of the helix are left unconnected. The wire diameter is 0.020 inch and the helix has 25 turns per inch. The wire 18, FIG. 1, is centered in the ferrite tube bore by two insulating plugs 30 and 35, FIG. 2, which fit the bore and are drilled for the wire. Such an arrangement is advisable at high pulse train frequencies in order to interpose space separating wire from the ferrite material, thus reducing capacitive loss.

Although these dimensions and specifications are preferred, they may be widely varied without extreme degra dation of results. The ferrite tube may have any length, but generally the effects produced thereby are proportional to its length. The ferrite tube external diameter may be varied, but should not be made so large that the ferrite occupies a major part of the volume of the waveguide. The wire helix may be replaced by a series of electrically conductive bands, such as the metal bands 34 of FIG. 3. The wire helix may also be replaced by a dielectric sleeve 36 as shown in FIG. 4, which is made of Stycast, made by Emerson-Cummings Co. This sleeve has an external diameter of three-eighths inch and a dielectric constant of 4.

The wire helix, when used, may be variously constructed of any conductive wire of gauge between 20 and 40 AWG, tinned or bare, spaced variously between turns. In general, spacing from the surface of the ferrite tube degrades the results in proportion to the amount of spacing. The permanent magnets 27 and 28, FIG. 2, may be positioned in aiding position, as in FIG. 3, instead of in opposing position as in FIGS. 2 and 4. Other means of applying a stationary magnetic field to the ferrite tube may be employed, examples of which will be given later.

In the operation of the embodiment of FIGS. 1 and 2, let it be assumed that microwave energy at a frequency of 8800 mc. p.s. is applied to the waveguide 12, and that the coaxial conductor terminal pairs 24 and 26 are unconnected. The applied microwave energy will then be available at the output waveguide 13 for application to a load, the device causing an insertion loss of about 0.3 db. Now let be supposed that a pulse train is applied between the terminals 24 and 26. This train has a frequency of 5000 c.p.s. and consists of rectangular 1 ,us. pulses. The maximum rise or fall time of each pulse is about 0.02 ,us. Measurement at the output microwave terminal 13 now discloses that during each pulse the energy available at the output terminal 13 is a few percent of the applied energy and that the degradation of the waveform is negligible. Thus the device constitutes a fast and efiicient on-ofi microwave switch.

These results show that the switch is operable up to a pulse train frequency limit of some 50 or 100 mc. p.s. and also may be employed down to a direct-current limit, that is, to switching by a single step change in direct current applied to the axial wire.

FIG. depicts another embodiment of the invention. A rectangular waveguide 37 is provided with sidearm 38 to constitute a shunt or H-plane T. The sidearm 38 is terminated in a movable plunger 39 constituting an adjustable short circuit. A ferrite component 41 is axially positioned within the sidearm 38. This component consists of a ferrite tube with a covering, and does not include the permanent magnet end cylinders shown in FIGS. 2, 3 and 4. Except for the absence of these permanent magnets, the ferrite component is identical with that described in connection with preceding figures. The ferrite component contains a central conductor 42, as before described. This conductor is terminated at one end on a cross wire 43 to which it is conductively secured. The cross wire 43 is positioned transvei'sely in the arm 38, and is secured to its narrow walls. This cross wire is thus perpendicular to the waveguide axis and to the narrow waveguide faces. The other end of the central conductor 42 is brought Out through the narrow wall 44 of the waveguide 37, the exit being provided with a choke to prevent escape of microwave energy. A metal sleeve 46 connected externally to the waveguide 73 at this point, surrounds and is insulated from the conductor 42 as it emerges and, with the conductor, constitutes a coaxial conductor terminal pair for the application of switching pulses or steps to the wire within the ferrite tube. The return of this circuit is, of course, through the material of the waveguide from the cross-conductor sidewall junction 33 to the tube 16. A permanent magnet 47 is positioned outside of the waveguide sidearm 38 parallel to the ferrite component 41 within. The permanent magnet 47 is secured to the broad face of the wavegmide sidearm 38 but is separated from it by a non-magnetic shim 48 of adjustable thickness. The purpose of this shim is to control the strength of magnetic field applied by the permanent magnet to the ferrite component.

In the operation of this device, microwave energy is transmitted from a source 49, through the waveguide 37, to a load 51. In the absence of current through conductor 42, the position of the short-circuiting plunger 39 is adjusted until a short circuit is reflected to the junction of the sidearm 38 with the waveguide 37. This distance is schematically indicated by the dimension D, and is equal to a multiple of one-half wavelength in the sidearm. The sidearm then does not interrupt the waveguide 37 transmission to the load 51. It now a direct-current step or pulse train be generated by generator 52 and applied to the wire 42, the circumferential magentic field around the wire 42 so affects the microwave properties of the ferrite component as to change the electrical length of the electrical path having the dimension D. The electrical length is caused to depart from a half wavelength multiple, and with an appropriate amplitude applied from generator 52 the electrical length is changed to an odd multiple of one-quarter wavelength in the waveguide. The input microwave energy now encounters an open circuit or high impedance at the sidearm, and energy transmitted to the load 51 is greatly reduced.

By changing the position of the plunger 39 the operation can be reversed, and energy will be transmitted to the load only when the wire 42 is energized.

FIG. 6 depicts an embodiment in which a rectangular waveguide is adapted to transmit microwave energy from one end 54 to the other end 56. A ferrite component 57 is of any one of the types described in connection with the preceding drawings. A stiff conductive wire 58 passes through the bore of the ferrite tube and is mechanically and electrically secured, as by welding, soldering, or riveting, at either end to two cross members 59 and 61. These members are also made of stiif conductive wire, and pass out of the waveguide through holes in the narrow side walls thereof, such as the hole 62. These holes may be protected by the usual choke constructions, not shown in the drawing. Insulating sleeves in the holes 62, or in the choke constructions if used, mechanically suppont the members 59 and 61, and through them and the wire 58 also support the ferrite component 57. The members 59 and 61 are at right angles, within the waveguide, to the microwave electric field, so that currents in the members cannot interact with the field. The waveguide 53 is surrounded, in the vicinity of the ferrite component 57, by a coil 63 having a pair of terminals 64 for connection to a direct-current source, whereby the coil generates a longitudinal magnetic field at the ferrite component.

It is possible, and may be advantageous in special cases, to combine any or all of the continuous magnetic field generating means described in connection with all six figures.

The waveguide 53, FIG. 6, is provided with two adjustable susceptan'ce matching or tuning devices. These devices may simply be screw stubs 66 and 67 in the median line of a waveguide broad face, adjustable in length between zero intrusion within the waveguide and an intrusion equal to not more than one-quarter wavelength in free space. The distance M between the screws is equal to an odd multiple of one-quarter wavelength within the waveguide between the screws. This wavelength in guide is determined under the condition of no current in the wire '58 but with the continuous magnetic field or fields in operation.

In the operation of this embodiment, with a directcurrent source connected to terminals 64, the screw 66 is adjusted for minimum voltage standing wave ratio between it and the microwave source connected to the waveguide end 54. Most of the microwave energy will then be transmitted [to the waveguide end 56 and out to the load connected thereto. The screw 66 will compensate for the discontinuities caused by the screw 67 and by the ferrite component and its supports. The transmitted bandwidth will be generally inversely proportional to the depths of insertion of the screws. If now a pulse train or a step current be applied to the support wires, for example to the ends 68 and 69, from the generator 71, the microwave transmitting properties of the section of waveguide containing the ferrite component will be modified during the step or during each pulse, with the result that the microwave energy reaching the load is reduced.

In some cases it may be desirable to employ a step or pulse modulation on the wire 58 which varies between two values of direct current instead of between zero and a single value. That is, continuous direct current and pulse current may be combined in the external circuit by means of frequency combination components, and the combined signal applied to terminals 68 and 69.

What is claimed is:

l. A microwave switch comprising, a rectangular waveguide shunt T having a main section and a shunt sidearm joined thereto, means for applying microwave energy to one end of said main arm, load means for extracting microwave energy from the other end of said main arm, a conductive plate short-circuiting the end of said shunt sidearm distal to said main section, .a [ferrite component positioned coaxially in said shunt sidearm, a permanent magnet positioned adjacent said ferrite component outside of said shunt sidearm, an electrical conductor extending axially through said ferrite component,

6 and means applying to said conductor a switching current having at any instant one of two magnitudes whereby when the current has one magnitude said main section is interdicted and when the current has the other magnitude said main section is microwave transmissive.

2. A microwave switch comprising, a rectangular waveguide, means for applying microwave energy to one end thereof, load means for extracting microwave energy from the other end thereof, a ferrite component positioned coaxially in said waveguide, discontinuity matching means positioned in said wave guide between one end thereof and said ferrite component, another discontinuity matching means positioned in said waveguide between the other end thereof and said ferrite component, a magnetizing coil wound around the outside of said waveguide adjacent said ferrite component and coaxial therewith, means applying direct current to said coil, an electrical conductor extending axially through said ferrite component, and means applying to said conductor a switching current having at any instant one of two magnitudes whereby when the current has one magnitude said waveguide is microwave transmissive while at other times said waveguide is nontransmissive.

3. A microwave switch in accordance with claim 2 in which said electrical conductor is connected at each end to one of two support conductors, the two support conductors being disposed at right angles to the electrical conductor, the support conductors conducting current to and from the electrical conductor and providing mechanical support, each support conductor penetrating a narrow side of said rectangular waveguide.

References Cited in the file of this patent UNITED STATES PATENTS 2,671,884 Zaleski Mar. 9, 1954 2,798,205 Hogan July 2, 1957 2,885,677 Zaleski May 5, 1959 2,906,974 Reggia Sept. 29, 1959 2,920,292 Scovil Jan. 5, 1960 2,951,220 Miller Aug. 30, 1960 2,994,841 Zaleski Aug. 1, 11961 FOREIGN PATENTS 202,013 Australia June 6, 1956 

1. A MICROWAVE SWITCH COMPRISING, A RECTANGULAR WAVEGUIDE SHUNT T HAVING A MAINS SECTION AND A SHUNT SIDEARM JOINED THERETO, MEANS FOR APPLYING MICROWAVE ENERG TO ONE END OF SAID MAIN ARM, LOAD MEANS FOR EXTRACTING MICROWAVE ENERGY FROM THE OTHER END OF SAID MAIN ARM, A CONDUCTIVE PLATE SHORT-CIRCUITING THE END OF SAID SHUNT SIDEARM DISTAL TO SAID MAIN SECTION, A FERRITE COMPONENT POSITIONED COAXIALLY IN SAID SHUNT SIDEARM, A PERMANENT MAGNET POSITIONED ADJACET SAID FERRITE COMPONENT OUTSIDE OF SAID SHUNT SIDEARM, AN ELECTRICAL CONDUCTOR EXTENDING AXIALLY THROUGH SAID FERRITE COMPONENT, AND MEANS APPLYING TO SAID CONDUCTOR A SWITCHING CURRENT HAVING AT ANY INSTANT ONE OF TWO MAGNITUDES WHERE BY WHEN THE CURRENT HAS ONE MAGNITUDE SAID MAIN SECTION IS INTERDICTED AND WHEN THE CURRENT HAS THE OTHER MAGNITUDE SAID MAIN SECTION IS MICROWAVE TRANSMISSIVE.
 2. A MICROWAVE SWITCH COMPRISING, A RECTANGULAR WAVEGUIDE, MEANS FOR APPLYING MICROWAVE ENERGY TO ONE END THEREOF, LOAD MEANS FOR EXTRACTING MICROWAVE ENERGY FROM THE OTHER END THEREOF, A FERRITE COMPONENT POSITIONED COAXIALLY IN SAID WAVEGUIDE, DISCONTINUITY MATCHING MEANS POSITIONED IN SAID WAVE GUIDE BETWEEN ONE END THEREOF AND SAID FERRITE COMPONENT, ANOTHER DISCONTINUITY MATCHING MEANS POSITIONED IN SAID WAVEGUIDE BETWEEN THE OTHER END THEREOF AND SAID FERRITE COMPONENT, A MAGNETIZING COIL WOUND AROUND THE OUTSIDE OF SAID WAVEGUIDE ADJACET SAID FERRITE COMPONENT AND COAXIAL THEREWITH, MEANS APPLYING DIRECT CURRENT TO SAID COIL, AN ELECTRICAL CONDUCTOR EXTENDING AXIALLY THROUGH SAID FERRITE COMPONENT, AND MEANS APPLYING TO SAID CONDUCTOR A SWITCHING CURRENT HAVING AT ANY INSTANT ONE OF TWO MAGNITUDES WHEREBY WHEN THE CURRENT HAS ONE MAGNITUDE SAID WAVEGUIDE IS MICROWAVE TRANSMISSIVE WHILE AT OTHER TIMES SAID WAVEGUIDE IS NONTRANSMISSIVE. 